Method of and apparatus for sound modification



R. M. WHITE May 7, 1935.

) METHOD OF AND APPARATUS FOR SOUND MODIFICATION Original Filed May 18, 1932 2 Sheets-:Sheet l RESt/L TA V RESUL TAIVT INVENTOR.

, 1 701501677 1 wfiz'fe ATTORNEY y 7, 1935- a R. M. WHITE 7 2,000,806

METHOD OF AND APPARATUS FOR SOUND MODIFICATION Ori gi nal Filed May 18, 1932 2 Sheets-Sheet 2 I 0 n o a I 6 o a a Q U .Q 0 0 D I O O I o o a a o o o a o a U Q Q 6 O i Q I I 0; 0 0 0 Q 0 I O I a p a o o o o 0 a 0 I U D 0 I U Q I} I I I D O O 0 O 0 0 I O f0. 7 INVENTOR.

ATTORNEYS.

Patented May 7, 1935 UNITED STATES PATENT OFFICE METHOD OF AND APPARATUS FOR SOUND MODIFICATION Richard M. White, East Cleveland,

Ohio, assignor to Macoustic Engineering Company, Cleveland,

Ohio, a corporation Application May 18, 1932, Serial No. 612,031 Renewed September 11, 1934 13 Claims.

The present invention, relating as indicated to a method of and apparatus for sound modification, is more particularly directed to a new, improved and simplified method and apparatus 5 for modifying sounds of various frequencies, in which the method employed involves the splitting of the sound waves into various components and the recombining of these components in a different phase relationship as distinguished from sound absorption as now generally practiced'by absorbing the energy of a sound wave or dissipating the energy of a wave by friction against a surface or within recesses r cavities in a surface;

To the accomplishment of the foregoing and related ends, said invention, then, consists of the means hereinafter fully described and particularly pointed out'in the claims; the annexed drawlugs and the following description setting forth in detail certain means and one mode of carrying out the invention, such disclosed means and mode illustrating, however, but one of various ways in which the principle of the invention may be used.

In vsaid annexed drawings:-

Fig. 1 is a diagrammatic view illustrating a view of a simple system of two sound waves; Fig. 2 is another view of a simple system of two sound waves of opposite phase combined to show a zero 30 resultantj Figs. 3 and 4 are diagrammatic views 1 illustrating in its simplest form my improved and novel method of sound modification; Fig. 5 is a similar view'showing a modified and more com plete form of apparatus embodying my method and 12 are other diagrammatic views illustrating heat through surface friction in the poresv or recesses of the absorbing material.

This method of sound absorption, while effective, does not. lend itself to convenient use, and in its use materials are ordinarily employed which gradually fill, up with dirt by reason of their necessarily porous nature, with the result that the absorptive value of the material is not constant of sound modification; and Figs,6', 7,8, 9, 10, 11v

and the material itself is not sanitary. In addition to these objections to the ordinary materials, it is difficult with'most of such materials to introduce decorative effects or to place the surface of the material in condition for cleaning or painting, as any surface coating applied thereto naturally tends to close the pores or recesses and thereby reduce the effectiveness of the materialasa sound-absorbing medium. I am aware of the use of material of the type which I have referred to as a-backing in a panel, in which the surface of the panel has an apertured hard plate provided with numerous minute openings through'which the'sound waves pass into the sound absorbing material behind the plate, and while this type of material presents an improvement for many purposes over the materials theretofore used, it still has the objections of relative 1y high cost, and a tendency to have its sound absorbing value reduced in use through the infiltration of dirt and foreign material. In addition to these objections, this type of sound absorbing material operateslupon the same principle of conversion of" sound energy into heat as r the other materials referred to above, and by these materials I include fabrics of-all sorts, compressed flbrous material, porous plasters and similar materialswhich have been employed for this al p pose.

My improved invention embodies a new and totally different method of sound absorption or modification, consisting essentially in the neutrali'zati'on of the intensity of sound reflected from a structurelby provid n that structure with means to reflect varying fractions of the incident sound wave, while'causing the reflected portions to differ in phase relationships with" the first or surface reflected'wa-ve. By' thus treating the sound waves as a combination of two or more waves of the same frequency traveling in the same direction but..havlng varying amplitudes I can produce a resultant sound wave of the same frequency, the amplitude of which will depend upon the phase relationships of the two or more original waves.- I have found it possible to provide apparatus which will combine the reflected portions of a so'undwave in such a manner that the phase relationships will cause a maximum of interfer'ence so that the resultant reflected wave will be much lower in intensity that the original. A classical example of the effect which I have found it possible to secure in the modification of sound'is found in the case of a tuning fork where there are-zones of varying loudness as the listening mechanism is moved around the surface, the; freflectegl w mitted therethr uehiiilie.

' which is reflected from mesu'ri: is: artially dicated by he. I; e

. reflected [rear platelE swag direction and having the-same, frequency.

amplitude, have the same phase the sound wave A is of a magnitude indicated in Fig. 1. If the second series of sound-waves B issuperimposed upon the first wave A so-"tlia'tthe phase difference is exactly 180 the resultant "sum of the two waves will be zero-rasmdicated'by-the line B, Fig. 2. If the twowaves arencombined: in phase with each other, then the sum willbe four times as great in intensity and twice as great in amplitude, as. either of the individualsound waves. .Theresultant is indicated-as a straight line B for the case where the two waves are i899 out of phase, in which .conditionthe soundimpulses have canceled or neutralized each other andno sensation of sound isperceptive to the human car, as the ear is sensitve Ito-vibratory: motions only and transmits assound only the re.- sult of motion-imparted to itby the vibrationof Withthis known principle as a basis, I- have developed-a methodv of at least partial neutra lig tion, or cencellation of. soundwaves produce,a reduction in the intensity ,of -sound, striking agemst a amina w ich heiferlo ed o effect this an el t staminawaves. Referring now to I have two surfaces D and. E from-each other,.

in. whichthe surface D a hard reflective,v si1r. face providedwitha series of openings therein.

A S un w Strikingsai sfl e i surface of the outer perforated plate D is partially reflected. therefrom; the reflected portion. indicated by the. line 4:, jand is "tram be-.-'

transmittedflthtougn the plate I) and r fle e rom; f I

. 17 4 11 hack iromthefplate D' by I ec -aw e Ystrikesin e e se ler fl sis ea m" A min h ovshthe plate I inclines n i e efiec fi PM e l n Z1 h m-deepe reflected' 'from-the plate E as-th liii eflj'z and o t se tren mit d menace D andindicatediby the, ,gr d on; he is reii." d ba imm e. Pie?? D indicated by tnel line a, in t a mittcd i b wave belittle-11y V efa'ainrene tecin theplat 'n, I hav foundjthat it desp rat -m s struct the. winner plate n o not over ape proximately- 2a%. maniac; r o a u a -i fo -199i h PQAW 2*???- approximately. 8Q%i to 96% ;95 the perforate amadetermmes thfi-p wfil fibti mt i assealamthepiato-niannxmeireqimn represented by the line w and this same amount of,- epergyis of coursereflected from the plate E Incl; toward the plate D. Of this amount 62% is transmitted through the plate D and is represented by the line 62% of 62%, or 38 is again reflected and again indicated by the line Y. If the phase relationship between the surface wave X, .which is reflected initially as the wave at, and the double reflected wave :r" is exactly 180, the sum of the two waves will have an amplitude of only one-half of 1% of the original unreflected wave.

:It is,then necessary only to account for the portion of the double reflected, wave thatwasfretumedfrom theinner side of the surface D to the surface E.; If Llet yrepresent the portion of; the sound ener y passed out of the system the manner indicated, it will have. .a valueoif 14.6% of .theoriginalwave since it isthe product of 3 8% 62 This. wave, however, phase withthe first reflected wave. and tends to augment theintensity thereof. The resultant of the first reflected wave with the second doublerefleeted wave and. the third wave .(xel bc +1.!) is 38%+14;-.6%38 %.,.or 14.1%.. Byaprly- S milar successive reflections to y em,

it Shown thatethe resultant intensity from aninfinite number 'of reflections closely.al pi7q1. i-. mates the value of 9.9 In other. words, thesyste n returns only'9. 9%fof the, sound incident inen alt ou h. there is no .d ss p t n s un thiiough friction, .and all of the dissipation or modificationnxerted on thefl'soiind vqav e is due entirely to the change in phase relations s. The phase relationships o-f; the various f corriponents is dependent. ,upon th e frequency of the original soumih the distahc efbetwepn the surfaces ei iEa-nd' h angle O i i q l sound ahsofbing panel consisting oflan, impei forate stes. spaced perforate. plate. ,1 ..',as. ,in' the form GI Fignii', andari additional spaced Per- I forate plate action .o.f -.this. construction 5 wi1 l -Ibe' similar. to, that diagrammatically illustrated in Fig 2f and-previously .desfiilihid', except that the sound retuiinedwill be stillfiii'tliei' mod if fiedby thespIi-ttine o hesoilpdw ve r hel s upon the "surface D, a fraction being reflectedand another fraction being. trans mitteg through-thejopeningsm the. plate. n1 The portion transmitted" will 'be leflccted from, the

plate E. will be returned in a different phase relatiomhip and therefore insuch a way as to modifythe reflected sound issuing fromthe str uc.- tureias a whole.

- InIE'i gQS, Ifhave ,shown a. similar structure cono e 2A of reflected. plate I! and perforated platesthat of Figs. 2' 'andfi, but will still more greatly nmdify reflectedw'aves'; Similarly the strucstil er od fying e fect.

.,.Whi1 e.;-I haveexplained that my system bf Fig 4, I have shown, ma i-emissary a.

I G arranged in spacedrelationship' l structu e will. of course have an efiect similar to ployed, in that the energy of the soundis not ab.-

sorbed, but is permitted to continue on and to be.

reflected in su'bstantially'its full intensity to neusound modifying or absorbing effect of my system by combining with it certain features of pre'-- vious systems. Thus in Fig; 7, for ex'ample, I

have shown a structure composed of a reflecting plate L and spaced perforate plate K, which will have the sound-modifying effect of the structure illustrated in Fig. 2. This effect can, however, be increased by coating the adjacent surfaces of the plates L and K with sound-absorbing material M. Either of the two adjacent surfaces of the plates L and K may be coated or both may be coated, and the amount of sound absorbed thereby will of course be deducted from the amount reflected, and by that amount the total sound reflected from the system will be reduced.

In Figs. 8, 9 and 10, I have shown perforated plates N, O and P, respectively, provided with variously shaped or sized openings R, S and T, respectively, and it will be evident that numerous arrangements of openings and forms of openings may be employed. I have found that the size and shape of opening can advantageously ,be varied, depending upon the frequency of sound vibration which is to be modified. Similarly, in a composite system or panel consisting of more than merely a single reflecting plate and a single perforated plate it is possible, by properly combining two or more plates provided with perforations, to modify sounds of different frequencies to greater advantage with plates having different sized and shaped openings and in this way to provide a composite unit which will have substantially any range of sound modification that is desired.

In Fig. 11, I have shown an apparatus for carrying out my improved system of modifying sound consisting of a substantially flat rear plate U and spaced perforated corrugated plates V and W. In this system it will be understood that the plates V and W are substantially parallel with each other and with the reflecting plate U as in the. constructions previously described, but it is not necessary that all of the plates be level or smooth and slight corrugations such as are indicated in the structure of Fig. 11 have no detrimental effect upon the sound modifying action of the system.

In Fig. 12, I have shown a structure very similar to that of Fig. 11 and consisting of rear reflecting plate U and perforatedplates V and W. The plates V and W in this structure,

however, each consists of a multiplicity of angularly related surfaces v and w. which are so related with respect to each other and of such area that they jointly form partially closed chambers H. Such a system has a greater phase distortion than a system of the structure shown in Fig. 4, consisting of flat, smooth plates and may therefore for certain purposes be advantageously used in preference to a structure employing flat plates only.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out and distinctly claim as my invention:-

1. In a method of modifying sound, the steps which consist in interposing in the path of a sound wave means capable ofp'artially reflecting and partiallytransmitting therethrough portions of said wave, and then reflecting the transmitted portions of such wave in a'phase"relationship diiTerent 'to that of the portion initially reflected.

2. Sound modifying apparatus consisting of two spaced plates, one'ofsaid platesbeing caps ble of partially tra'nsmittingand partially reflecting sound waves incident ther'eupon-, and'the' other of said plates being capable of reflecting the transmitted portions of sound waves passing through said first-named plate in a phase relationship different from that of the wave portion reflected from'the first-named plate.

3. Sound modifying apparatus consisting of a series of spaced perforated plates, each of said plates being capable of transmitting a portion of the sound wave incident thereupon and of reflecting the remainder of such sound wave.

4. Sound modifying apparatus consisting of an imperforate plate, a plurality of perforate plates disposed approximately parallel to said imperforate plate and in spaced relationship therewith and with each other, said perforated plates being each capable of transmitting a portion of a sound wave incidentally and of reflecting in a difierent phase relationship the remainder of said sound wave.

5. Sound modifying apparatus consisting of an imperforate sound reflecting plate and a second perforated plate disposed approximately parallel to said imperforate plate, one of said plates being providedwith sound absorbing means on the surface adjacent to said other plate.

6. Sound modifying apparatus consisting of an imperforate plate and a plurality of perforated plates arranged in spaced parallel relationship with said imperforate plate, said perforated plates having openings therein of different size and form and being capable of producing splitting of the sound wave incident thereupon and of producing interference with the reflected portions of sound waves of different frequencies.

'7. Sound modifying apparatus consisting of an imperforate sound reflecting plate, and a second perforated plate disposed approximatelyparallel to said imperforate plate, each of said plates being provided with sound-absorbing means on the surface adjacent to said other plate.

8. Sound modifying apparatus consisting of an imperforate sound reflecting plate, and a second perforated plate disposed approximately parallel to said imperforate plate, each of said plates being provided with sound-absorbing means on the surface adjacent to said other plate.

9. A sound modifying apparatus consisting of an imperforate sound reflecting plate, and a second perforated plate disposed approximately parallel to said imperforate plate, one of said plates being provided with corrugations.

10. Sound modifying apparatus consisting of an imperforate sound reflecting plate, and a plurality of perforated plates arranged in spaced parallel relationship with said imperforate plate, said last-named plates being provided with corrugations.

11. Sound modifying apparatus consisting of an imperforate sound reflecting plate, and a plurality of perforated plates arranged in spaced parallel relationship with said imperforate plate,

said perforated plates having openings therein of different size and form and one thereof being provided with phase-distorting corrugations.

12. Sound vl'smliitvinz, apparatus consisting a; an imperial-ate sound reflectiaa plate, a pluralitr of perforated plates maimed in spaced,

parallel relationship with said imperforate plate, -5 said last-namedvplates being provided with corrugations and the corrugations in adjacent plates being so mined as to form partially. closed 13. Sound modflyina apparatus consisting of III. on imp ial-etc plate provided with sound absorbing material on one surface thereof, and a plurality. of perforated plates arranged in spaced parallel relationship with said imperforate plate,

the surfacesof said last-named plates facing the coated surface ofsaid imperforate plate being provided with sound-absorbing material, and said last-named plates being provided with corrugations arranged to form partially closed chambers between adjacent plates. 1

' I RICHARD M. WHITE. 

